Froth flotation process and apparatus



P 1967 v. A. ZANDON ETAL 3,343,674

FROTH FLQTATION PROCESS AND APPARATUS Filed Feb. 23, 1965 KW? 13. a,

m A ni United States Patent Ofiflce 3,343,674 Patented Sept. 26, 19673,343,674 FROTH FLOTATION PROCESS AND APPARATUS Victor A. Zandon,Carlsbad, N. Mex., J. Stanley Mitchell,

Vicksburg, Miss, and Charles W. Abernethy and Milton H. Klein, Carlsbad,N. Mex., assignors to American Metal Climax, Inc., New York, N.Y., acorporation of New York Filed Feb. 23, 1965, Ser. No. 434,392 7 Claims.(Cl. 209-166) ABSTRACT OF THE DISCLGSURE Froth flotation machine havingend walls and side walls. On'fices are located in side walls on a levelsubstantially corresponding to the froth-liquid interface and areadvantageously located in upper portion of the side walls intermediatethe ends walls. Also disclosed is a process for recovering coarsersylvite particles by longitudinally moving pulped ore through flotationapparatus and transversely removing sylvite from the froth over thelateral edges of the apparatus while transversely withdrawing coarserparticles at a lower level which corresponds to the frothliquidinterface without disturbing the relative quiescence of the interface.

This invention relates to an improved method and apparatus for effectingthe recovery of sylvite values in differential froth flotationprocedures.

More particularly, the present invention relates to the recovery ofcoarse sylvite crystals, and especially those concentrated by frothflotation within the resulting pulp liquid-froth interface, by means ofnovel froth flotation apparatus.

' Recovery of sylvite values from sylvinite ores by differentialflotation processes from a finely ground (eg. all minus 28 mesh)sylvinite ore, moderately well deslimed and conditioned or reagentizedby conventional techniques, has been accomplished effectivelyheretofore. Levitated in these known procedures by air bubbles,individual finely ground sylvite crystals concentrate in a froth columnusually of about two inches to four inches in depth above the pulp levelof the cell. The froth con taining the fine sylvite values is removed byrotating paddles into the overflow launders and recovered.

Where the sylvinite ore contains a wide range of crystal sizes rangingfrom coarse through fine, e.g. minus 8 to about 200 mesh, the flotationsequence involves floating and recovery of the sylvite values of minus28 at the head of the flotation unit as described above. Intermediatesizes of sylvite mineral values within the range of minus 12 to 28 meshare next floated and removed; the concentration of the intermediate sizeparticles taking place in a much shallower froth column than that forthe fine size particles. The particles of minus 8 and +14 mesh, i.e.,the coarse particles, are then recovered in varying amounts but withsignificantly less efliciency in the remainder of the flotationapparatus. During this latter concentration and recovery phase, thedepth of the froth column is minimal. Thus, those coarse crystals ofsylvite values which are successfully floated are present on the surfaceof the liquid phase as an agglomerated layer, one particle deep. Thisagglomerated layer is supported by a multitude of fine air bubbles; theconcentration and recovery technique employed being designated as skinflotation. As will be apparent and as is otherwise commonly known, aprerequisite to even relatively successful skin flotation is therelative quiescence of the surface in the flotation unit or machine.That is, the surface must present a substantially unbroken continuum offine air bubbles with suspended sylvite values therein. Any materialdisturbance of this surface causes a rupture of the air bubble-mineralagglomerates with the consequent sinking of the coarse particles presenttherein. Inasmuch as the coarse sylvite crystals are very diflicult tolevitate in any event, the losses of such particles in the tailingportion of the flotation pulp are greatly increased by such surfacedisturbances.

The difficulties in obtaining suitable quiescence for skin flotationresult principally from the relative inability known heretofore ineffecting proper baflling of the vertical and horizontal circular pathsdefined by the contents of the flotation cells and resulting from theaction of the agitating mechanisms and the introduction of air to effectformation of the desired froth.

Exceptionally coarse textured mineral values, i.e. sylvite, of theflotation feed, arising from the current demand for larger particlesizes thereof for consumer use, thus imposes even more stringentlimitations on downward adjustment in speed of the impellers used inaccomplishing agitation of the conditioned pulp feed as well as in thevolume of compressed air used. Indeed, insufiicient agitation andaeration invariably accelerate the sanding of the flotation cells withconsequent cessation of the skin flotation operation.

Accordingly, it has now been discovered that deep agitating flotationcells, such as the deep air cell, for example, the Munro-Pearse deepflotation cell, are ably adapted for use in the concentration ofnonmetallic mineral values, such as sylvite, and obviate the aforesaiddifficulties relating to undue disturbance of the surface of the liquidsuspension present in the flotation unit. Indeed, the use of theseso-called deep cells provides the desired quiescence of the surfacethroughout the length of the flotation unit at the interface between theliquid and froth of the conditioned pulp. However, where, for example,even five or six standard deep cells are used in a flotation unit ormachine, the skin flotation condition, very much in evidence in the lastthree cells of such a unit, is not sufflciently effective as a means forrecovery of the coarse particles of the pulp. Attempts to inducetransverse motion of the agglomerates provided by skin flotation, as,for example, by use of paddles, to accomplish their passage over the lipof each of the last two or three cells of a six cell flotation machineand into the launders positioned thereunder have evidenced only alimited degree of elficacy.

It has been further discovered, however, that the concentration andrecovery. of the coarse particles of desired sylvite values can,surprisingly, be very effectively accomplished by providing a pluralityof orifices at the level of the liquid-froth interface of certain of theflotation cells of the flotation machine, defining passage between thecell compartment, in each instance, and the adjacent launder. Theseorifices disposed in a horizontal plane parallel to the upper lip oredge of theflotation unit provide the machine with the necessarystructure to recover substantially all of the coarse par-.

ticles of mineral values since the concentration of coarse sylvitevalues occurs initially at the aforesaid interface between liquid andfroth, particularly in the very shallow froth of the intermediate cellsof the flotation unit or bank.

These and other significant objectives and advantages of the presentinvention will become evident in the course of the detailed descriptionappearing hereinafter considered in concert with the accompanyingdrawings, showing an illustrative embodiment of the invention.

In the drawings:

FIG. 1 is a cross-sectional semidiagrammatic repre sentation taken online 1--1 of FIG. 2 of an illustrative 8 3 deep flotation cell for usein the practice of the invention; and

FIG. 2 is a fragmentary isometric view of a series of ,cells forming oneflotation machine.

Referring more particularly to the accompanying drawings in which likenumbers in the written description and drawings designate like parts,reference is made initially to FIG. 1 where, in a deep agitationflotation cell 5, disposed at the head of a flotation unit 6, includinga bottom wall 7 and upstanding side walls 8, air enters the pulpconditioned in standard manner with -a nonmetallic mineral collectingagent and, if desired, a froth flotation oil and slime inhibitingreagent, by means of the hollow impeller shaft 9 with an air connectionto the air header 11 which, in turn, receives its high pressure airsupply from a compressor (not shown). The air forced into the impellershaft is disseminated through and below the fin; gers 12 of impeller 13in the form of minute bubbles. These are mixed vigorously with the pulpand the mixture aerated in this manner travels downward, outward,upward, and through the main body of pulp present in cell 5. As theareated pulp leaves the impeller zone, the mass of bubbles take theshortest path to the surface where the sylvite values collectedbybubbles form a froth column 18 or a layer on the upper surface.

The aerated pulp is thus passed to the surface of the cell wherein aZone of relative quiet obtains. The aerated pulp, as a result, readilyliberates the bubbles present therein which have been mineralized withthe desired sylvite values. These bubbles rise, as a result, to form thefroth column 18. The liberated and mineralized bubbles from the frothwhich is limited only by the side walls 8. Thus, the froth isdistributed across the width as well as the length of each cell, and isinterrupted in each instance only by the impeller shaft 9 in each cell.

The froth containing the desired sylvite values, for example, arerecovered in the launders 19 which are conduits disposed exterior to theupper portion of the side walls 8.

At the head cell 5a wherein the pulp is introduced in a standard mannerand aeration initially occurs, fine sylvite values are recovered in thefroth which passes over the rim or overflow lip 21 of the side wall 8.These values are of about minus 28 mesh, and in the procedure, thusemployed, is well-known in the art as described hereinabove.

The head of the unit 6 composed of the cell 5a, and normally a secondcell 5b as well, are continuous with each other and with a plurality offurther cells, normally three to four in number, which combine to formthe flotation unit or machine 6. Each of these cells contains animpeller, e.g., a standard Galligher or Denver impeller, for maintainingagitation of liquid pulp. The froth becomes measurably shallower insucceeding cells and contains intermediate sized sylvite values in therange normally of about 12 to 28 mesh in the intermediate zoneencountered along the length of the flotation unit. In the standardunit, the column of froth attains a height of about .25 inch to .5 inchin this intermediate zone, which extends for about the middle one-thirdto one-half of the length 'of the entire flotation unit.

The ultimate object of flotation procedure is to obtain a quiescentsurface conductive to skin flotation and heretofore revolving paddles(not shown) are used on both sides of the cells to push the froth andvalues therein into the launders. However, the paddles break thedesirably continuous quiescent surface which is particularly harmful ifthe paddle depth extends below the froth into the liquid state. Thedetailed description to this point is obviously directed to structureand processes well known to the art, it being recognized that deep cellscan more easily produce desirable skin flotation.

While the froth layer floats fine particles, the more desirable heavierand coarser particles tend to accumulate as a thin film, one particlethick, just beneath the surface of the liquid stage which is below thefroth column. If this film is broken or disturbed, the heavy particlestherein rapidly sink and are lost. It has been found that these heavyparticles are more effectively recovered by inducing transverse motionat the thin film layer without breaking the film while on the cell.

Accordingly there is shown a preferred method herein of inducingtransverse flow. The outer walls 8 of -cells 5c and 5d contain aplurality of orifices 22 at the froth-liquid interface which thustransmit sylvite values of 8 mesh and coarser from cells to the launder19. The orifices 22 are disposed along a substantially straighthorizontal line above the bottom or base of the launder and below therim or overflow lip 21 of the cell walls 8 and parallel therewith. Inintermediate cells 50 and 5d, the orifices occur normally at a depth of1 to 2 inches below the lip or top of froth.

The orifices are here shown for the middleone-third of the entire unitand it has been found more eflicient to include orifices for the middleone-half to one-third of the unit. However, they can be incorporatedalong the entire length of the unit with somewhat less effectiveness..

The position or level of the orifices along the entire unit will varyfrom about /2 to 3 inches below the lip or top of the froth, the greaterdepths being at the feed end because the froth is thicker at that end.

The diameter of the orifices may be from A to 1 inch, depending somewhaton the number. As shown in cells 5c and 5d there are 21 orifices on eachside (10 feet for 2 cells) which are 1% inches below the lip. Theseorifices may be replaced by intermittent or continuous slots at theappropriate level. In fact, any means of inducing transverse flowwithout breaking the skin surface on the liquid at the interface iswithin the scope of this invention. Where the transverse flow is to beinduced only on intermediate sections, e.g. cells 50 and 5d, the lipsmay be lowered in those sections to the point just below theliquid-froth interface to induce the desirable flow.

The launders 19 lead to a common source for subsequent screening ofparticles to desired size but particle classification could be at leastpartially accomplished by isolating the flow from the various cells andparticularly that from 50 and 5d.

As indicated hereinabove, the removal of the mineral particles presentat the foregoing interface in accordance with the preferred practiceherein described results from the initial concentration of coarseparticles, that is those sylvite values of from about 8 to 14 mesh, atthis level in the intermediate zone. At the same time, the intermediatesizes of sylvite in the range of about 12 to 28 mesh are present in thefroth above the aforesaid interface, in the intermediate zone of theflotation unit, and are recovered simultaneously with the coarserparticles passed through the orifices, in the launders, by passage offroth containing the intermediate size sylvite values over the overflowlip. It will be apparent that a variable quantity of sylvite valueshaving a mesh size of 12 to 14 is transmitted to the launder by eitheror both means, that is in the overflow of froth or by transmission fromthe concentratoin of particles at the liquid-froth interface.

Thus, the remainder or terminal end of the flotation bank, comprisingabout one-third of the unit length normally (and not less thanone-fourth) and encompassing cells 5e and 5 of a six cell bank orflotation unit,'is employed to effect recovery of any stray coarsesylvite particles which may have escaped recovery in the foregoingintermediate zone. This scavenging action in the terminal or tail end ofthe unit is accomplished by skin flotation as described above.

The methods employed in processing a mined sylvinite ore for productionof a conditioned pulp to be subjected to flotation in the mannerdescribed'he-rein may vary widely, but will include, by way ofillustration, the tech niques and methods described and alluded to inapplication Serial No. 320,388, now Patent No. 3,282,418, andapplication Ser. No. 363,405, now Patent No. 3,310,170, filed on Oct.31, 1963, and May 18, 1964, respectively, by Abernethy and Klein, two ofthe inventors of the subject matter herein described and claimed. 5While the present invention has been described in terms of deepagitation cells such as the deep air cell, it should be apparent thatconventional shallow pneumatic flotation cells, such as the ForresterCell, can also be employed, but are markedly less preferred due to thedisturbance caused not only on the surface of the pulp treated in suchcells, but even more significantly, because of the disturbance incitedat the liquid-froth interface in the intermediate treatment zonedescribed above. The advantages inherent in the use of the deep air cellare many, as have been made manifest in the foregoing description, andinclude not only thorough aeration of the pulp, but greater opportunityfor froth formation due to enhanced and longer periods of quiescence; amore compact and stable froth; an increased capacity per lineal foot ofcell and unit; higher recovery of mineral values and more efiicientoperation; and the absence of a tendency of the unit to choke under evenadverse conditions.

A preferred deep flotation machine or unit, for purposes of furtherillustration, for use in the practice of this invention, is one havingan approximate length of 30 feet, a width of 9 feet, 6 inches and adepth of 6 feet, as opposed to a 3 foot, 4 inch depth and a width of 7feet in conventional shallow flotation machines.

Thus, a preferred ratio of length and depth in the flotation machinesemployed herein is in the range of 4 to 6 (length):1 to 2 (width):l(depth); the most significant relationship being that of length to depthwhich may be expressed by the range, respectively, of 4 to 6:1.

The significance of the increased efliciency in recovery of nonmetallicmineral values, and particularly sylvite values, employing the inducedtransverse flow via the orifice-punctuated intermediate treatment zoneof the present invention to effect transverse movement of theconcentrate of coarse particles, is particularly marked when observed inthe standard commercial milieu where cost is extremely critical and theflotation of vast quantitles of nonmetallic mineral values are involved.

Operation of a commercial deep 6-cell unit with the orifices on themiddle two cells open as shown in the drawings and subsequently closedgave the following comparative results:

O RIFICES OPEN recovering mineral values of a coarse, intermediate andfine particle size from a liquid pulp containing such values whichcomprises a bottom wall, end walls and side walls, each of said sidewalls having an upper portion with a substantially horizontalfroth-overflow edge and a liquid pulp fr0th interface level which isbelow said edge and substantially parallel thereto and at least one ofsaid side walls having a plurality of orifices for receiving andcarrying coarse particle size mineral values therethrough to a launder,said orifices being substantially horizontally disposed in the upperportion of said Wall along said interface level.

2. A froth flotation machine as claimed in claim 1 wherein opposed sidewalls are provided with a plurality of orifices for receiving andcarrying coarse particle size mineral values therethrough to launderslocated on each side wall.

3. A froth flotation machine as claimed in claim 2 wherein said orificesare 4 inch to 3 inches on center below the froth-overflow edge of eachopposed side wall.

4. A froth flotation machine as claimed in claim 3 wherein each of theorifices is circular in cross section and has a diameter ranging from Ato 1 inch.

5. A froth flotation machine as claimed in claim 4 wherein said machineis formed of a plurality of longitudinally aligned deep air cells andwherein said orifices are disposed along the middle third to middle halfof the length of the side Walls of said machine.

6. A process for improving the recovery of coarse particle size sylvitevalue from sylinite ores in a liquid pulp condition which comprisesplacing said sylvinite in a flotation enclosure having an open top andsides containing overflow edges, producing a froth column containingsylvite values atop the liquid of the liquid pulp and producing aquiescent interface zone containing coarse sylvite particles between thefroth column and the liquid, longitudinally moving said liquid in theenclosure and transversely removing sylvite values from the froth columnover the overflow edges of the sides of the enclosure without disturbingthe quiescence of the interface zone While transversely removing coarseparticles contained in the interface Zone through orifices located at alevel below that at which the sylvite values from the froth column areremoved.

7. The process as claimed in claim 6 wherein the coarse particles aretransversely removed from the enclosure intermediate the ends of theside walls.

Feed Concentrate Tailings Percent K 0 Recovery Percent Percent PercentPercent Percent Percent weight K20 weight K20 weight K20 10 Mesh- 20.119. 1 10. 9 61.18 22.2 2.88 89.3 10 Mesh-" 79.9 22.77 89.1 55. 94 77.89. 66 9. 83

Total- 100. 0 22. 0a 100. 0 56. 52 100. 0 1.15 96. s

ORIFIOES CLOSED 10 Mesh. 1s. 4 1s. 70 12. 0 61.16 20. 3 4. 77 80.8 10Mesh. 81.6 22.87 88. 0 56. 57 79. 7 0. 79 97.9

Total. 100. 0 22.10 100. 0 57. 12 100. 0 1.58 95. 5

Thus, there is an absolute increase in KCl recovery References Cited andalso in the recovery of the more valuable +10 mesh product. At presentprices, a plant having an annual UNITED STATES PATENTS production levelof a million tons would have an annual 2,316,770 4/ 1943 Daman t a1209-169 increased sales value of about $300,000. 2,931,502 4/1960Schoeld et al 209170 X Various modifications of the invention can bemade and to the extent that such modifications and variationsincorporate the spirit of this invention, they are intended to beincluded within the scope of the appended claims.

What is claimed is:

1. A froth flotation machine particularly adapted for HARRY B. THORNTON,Primary Examiner. TIM R. MILES, Examiner.

L. EATHERTON, Assistant Examiner.

1. A FROTH FLOTATION MACHINE PARTICULARLY ADAPTED FOR RECOVERING MINERALVALUES OF A COARSE, INTERMEDIATE AND FINE PARTICLE SIZE FROM A LIQUIDPULP CONTAINING SUCH VALUES WHICH COMPRISES A BOTTOM WALL, END WALLS ANDSIDE WALLS, EACH OF SAID SIDE WALLS HAVING AN UPPER PORTION WITH ASUBSTANTIALLY HORIZONTAL FROTH-OVERFLOW EDGE AND A LIQUID PULP-FROTHINTERFACE LEVEL WHICH IS BELOW SAID EDGE AND SUBSTANTIALLY PARALLELTHERETO AND AT LEAST ONE OF SAID SIDE WALLS HAVING A PLURALITY OFORIFICES FOR RECEIVING AND CARRYING COARSE PARTICLE SIZE MINERAL VALUESTHERETHROUGH TO A LAUNDER, SAID ORIFICES BEING SUBSTANTIALLYHORIZONTALLY DISPOSED IN THE UPPER PORTION OF SAID WALL ALONG SAIDINTERFACE LEVEL.
 6. A PROCESS FOR IMPROVING THE RECOVERY OF COARSEPARTICLE SIZE SYLVITE VALUE FROM SYLINITE ORES IN A LIQUID PULPCONDITION WHICH COMPRISES PLACING SAID SYLVINITE IN A FLOTATIONENCLOSURE HAVING AN OPEN TOP AND SIDES CONTAINING OVERFLOW EDGES,PRODUCING A FROTH COLUMN CONTAINING SYLVITE VALUES ATOP THE LIQUID OFTHE LIQUID PULP AND PRODUCING A QUIESCENT INTERFACE ZONE CONTAININGCOARSE SYLVITE PARTICLES BETWEEN THE FROTH COLUMN AND THE LIQUID, LONGI-